Service triggers associated with a subscriber may be set at a switching office and can include originating call attempt triggers, terminating call attempt triggers, and various other types of service triggers. These triggers may be fired/activated at a switching office based on an attribute of the call (e.g., inbound, outbound), the called or calling party associated with the call/call attempt, or other call attributes that are well known to those of skill in the art.
The switching office (e.g., a service switching function (SSF) or service switching point (SSP)) acts as the trigger point for further services to be invoked during a call. The SSP implements the basic call state machine (BCSM) which is a finite state machine representing an abstract view of a call from beginning to end (off hook, dialing, answer, no answer, busy, hang up, etc.). As each state is traversed, the exchange encounters detection points (DPs) at which the SSP may invoke a query to the SCP to wait for further instructions on how to proceed. Trigger criteria are defined by the operator and might include the subscriber calling number or the dialed number. The SSF is responsible for entertaining calls requiring value added services.
The call model is a generic representation of SSP call-processing activities required to establish, maintain, and clear a basic call. The call model consists of point in calls (PICs), detection points (DPs), and triggers. PICs represent the normal switching system activities or states that a call goes through from origination to termination. For example, the null state or the idle state is when the SSP is actually monitoring the customer's line. Other examples of states, or PICs, are off-hook (or origination attempt), collecting information, analyzing information, routing, alerting, etc. In the AIN call model, trigger detection points (TDPs) are located between the PICs and SSPs are configured to check TDPs to see if there are any active triggers.
There are three types of triggers: subscribed or line-based triggers, group-based triggers, and office-based triggers. Subscribed triggers are provisioned to the customer's line so that any calls originating from or terminating to that line would encounter the trigger. Group-based triggers are assigned to groups of subscribers. Any member of a software-defined group will encounter the trigger. Office-based triggers are available to everyone who is connected to the telephone switching office or has access to the North American numbering plan. Office-based triggers are not assigned to individuals or groups.
If an active trigger is detected, normal switching system call processing is suspended until the SSP and SCP complete communications. For example, in the diagram above, suppose an AIN call has progressed through the null state or the off-hook PIC and is currently at the collecting-information PIC. Normal call processing is suspended at the information-collected TDP because of an active off-hook delayed trigger. Before progressing to the next PIC, the SSP may assemble an information-collected message and send it to the SCP over the SS7 network. After SCP service logic acts on the message, the SCP may send an analyze-route message that tells the SSP how to handle the call before going to the next PIC (analyze information). Essentially, when the SSP recognizes that a call has an associated AIN trigger, the SSP suspends the call processing while querying the SCP for call routing instructions. Once the SCP provides the instruction, the SSP continues the call model flow until completion of the call.
One problem associated with conventional trigger activation is that each switching office in the network has to be provisioned and maintained with a current, up-to-date list of all subscribers subject to a particular service in order to determine and effectively communicate to whom the service should be applied. This can result in an undesirably high administrative burden on the part of network operators.
Accordingly, in light of these difficulties, a need exists for reducing the administrative overhead associated with activating IN/AIN service triggers at a switching office without requiring that the switching office be provisioned and maintained with a current, up-to-date list of all subscribers subject to a particular IN/AIN service.